A typical apparatus for longitudinally cutting a longitudinally moving web has a pair of blades, normally termed upper and lower blades although side-by-side horizontal orientation is equally possible, that ride on respective transverse guides that both extend parallel to each other crosswise of the goods being cut. The web passes between the guides and the two blades are positioned immediately adjacent or even in contact with each other to cut the web.
Each blade is normally a disk rotatable about an axis perpendicular to the longitudinal direction of travel of the web and is carried on a respective holder that can slide transversely along the respective guide. A respective spindle is threaded through a nut in each such holder, with these spindles extending parallel to the respective guides and, therefore, parallel to each other. The two spindles are furthermore connected together for joint synchronous rotation so as to move the respective guides transversely in order to change and set the positions of the respective blades. This makes it possible to vary the widths of the strips being cut from the web.
When the device is in use the holders are invariably subjected to some forces parallel to the guides. Since the motors for the spindles are disconnected from them except during an adjustment operation, this can back drive these motors, thereby throwing the cutters out of position.